SE-SKOLORNAS 1978 Problem 2

Let $s_m$ be the number $66\cdots 6$ with $m$ digits $6$ . Find $s_1 + s_2 + \cdots + s_n$

Dataset text AI-MO AoPS. Quoted with source.

Solutions

No solution is on olymmath yet. Official and human solutions come first when they arrive. AI solutions come after them, with a label.